This is for people (like me) who leave things behind every where they go. I'm hazy on the details of the technology but it would probably involve similar tech to magnetic anti-theft devices in stores, or maybe in the future cheap / tiny chips with RF transceivers. Basic idea is a central device which uses weak (and therefore quickly degrading) radio signals to repeatedly "ping" a set of passive radio stickers in its neighbourhood. You put the central device on your belt / around your neck / on your wrist / through your bellybutton and a sticker on each personal item you carry around. If a sticker goes outside the range (a few feet) the return signal drops, and the device beeps. Future enhancements would use active chips on stickers with ID numbers, so the device could tell you what was missing; and direction sensing so it could tell you where. Another enhancement would be something which gave you electric shocks to train you to not lose stuff in the first place.-- bumhat, Sep 06 2002 Radio Frequency Identification Tag technologies http://www.aimgloba.../technologies/rfid/What you describe is pretty baked. [bristolz, Sep 06 2002, last modified Oct 04 2004] Purse Guard http://www.purseguard.homestead.com/Somewhat larger than a sticker, but... [egnor, Oct 04 2004] RFID tags-- bristolz, Sep 06 2002 Ah. Of course it is.-- bumhat, Sep 06 2002 Could get annoyig if you put one on your mobile and leave it downstairs to charge, go to sleep upstairs and have to put up with your belt's hushed bleeping all night.-- kaz, Sep 06 2002 Great idea. But the return signal wouldn't have to be generated constantly. You could have a "Have I forgotten anything button". If the answer is yes, it will tell you what items it doesn't see. Then a signal gets broadcast and the sticker will start beeping when the base unit comes within a few metres of it. This is good for when you've left your phone under a bunch of papers or something. So you could find something if you have lost it, as well as being reminded to take things with you. Of course the aggrevating thing would be forgetting to take the actual device with you, thus forgetting a whole bunch of other stuff too. Perhaps as well, there could be a proximity detector that automatically activates the device when you go into a certain area - up to the front door, when you get into your car etc.-- DiamondJo, Oct 03 2002 Great idea - I thought of it years ago while working on RFID. Have a prototype working that incorporates many of features you mention, plus a few more. Patent applied for and waiting for technology of tags to catch up.-- dlinnk, Dec 24 2002 random, halfbakery